Import lead sheets / standards with one function

[jarmitage]

References:

• ireal voicings #653
• stateless voicings + tonleiter lib #647
• https://loophole-letters.vercel.app/ireal-changes

Strudel supports ireal chord syntax, and there's 1000s of standards online, and we can parse them.

It would be great to support a potentially large dictionary of standards within a function, e.g. standard("song_name"), which could set among other things:

• Tempo
• Key
• Chords
• ???

This would give Strudel users rapid access to high level musical structure, which they could quickly build an arrangement out of, and start orchestrating/remixing/etc.